The invention relates to a method for controlling the lighting of a display in an electronic device, in which method ambient light is led to a light-sensitive component of the device through a light guide, the light-sensitive component controlling a display illuminator lighting the display on the basis of the ambient light.
Further, the invention relates to an electronic device that comprises a display element, a protective display window arranged to protect the display element, at least one display illuminator, a light-sensitive component arranged to control the illuminance of the illuminator on the basis of ambient light, a light guide leading ambient light from the surroundings of the device to said light-sensitive component.
The electronic devices—later in this application referred to as ‘device’—mentioned in this application are typically for instance mobile stations, such as mobile phones or communicating devices, or electronic games, combinations of the above or other corresponding devices. What said devices have in common is a display, for instance liquid crystal display, that is lighted by a background light, front light or both. The lighting of the display is intended to improve the clarity and visibility of the display in different lighting conditions.
Arrangements are known, in which the lighting intensity can adjust itself automatically according to the ambient light, thus providing automatically optimal display lighting in different lighting conditions. In these arrangements, ambient lighting is typically detected by a component reacting in some manner to a change in lighting. Such light-sensitive components include light emitting diodes, phototransistors and photoresistors. Such a component—later referred to as light-sensitive component—is usually quite vulnerable and, therefore, it is preferably fitted inside the device. A light guide is arranged between the light-sensitive component and the outer surface of the device, through which ambient light enters the light-sensitive component. The light-sensitive component reacts to the ambient lighting conditions on the basis of the light coming through the light guide, and adjusts the display lighting.
A problem with the arrangement described above is that the light guide is a small and transparent component and very difficult to handle in production and the assembly of the device. The light guide requires fastening elements for fastening it to the device and a work stage, during which the light guide is fastened to these fastening elements. In addition, the light guide requires a seal for sealing the joint surface between the light guide and the device casing against moisture and dust. For said reasons, costs accrue from the light guide during component manufacture as well as device assembly. Yet another prior-art problem is that the air gap between the light guide and the rest of the device reduces the ESD (electrostatic discharge) shielding: an ESD spark can enter the device through the gap, thus endangering the electric components of the device.
U.S. Pat. No. 5,384,577 discloses a different type of solution, in which a liquid crystal display is lighted by an electroluminescent panel fitted behind it. The electroluminescent panel also has a second function: it serves as a light-sensitive component that detects ambient lighting and switches the display lighting on when the ambient lighting is below a certain limit value. Such a solution is quite expensive and complex.